Ruggedized attenuator insert



Filed March 15, 1957 N MH N as sound waves and radiowaves.

United States Patent RUGGED'IZ'ED 'ATTENUATOR INSERT Joseph M. Schramp, Rome, N.Y.,'as signor to the United States of America .as represented by the Secretary of the Air Force :Application-Marck-IS, 1957, Serial No. 646,509

'9 Claims. (Cl. 338 -309) (Grantednnder Title 55, U.S.;Code (1952), sec. 266) The inventiondescribed herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to an attenuator insert article and method and more particularly to a more rugged attenuator insert than has been available heretofore and to the method by which it is made.

An attenuator, according to the Cooke and Markus Electronics Dictionary, published in 1945 by McGraw- Hill Book Company, Inc., New York city, New York, is an arrangement of variable resistors used to reduce the strength of an audio-frequency or radio frequency signal a desired amount without causing appreciable distortion. The corresponding nonadjustable device'is called a. pad. Attenuation is a decrease in the intensity of energy, such A discussion on attenuators which is adequate for an understanding of the background of the pr'esentinventionis'presented in the Radiation Laboratory Series, volume 11, published in 1947 by McGraw-Hill Book, Inc., New York city, New York. At page 745 in that text is described carbon powder in oil painted on a glass or ceramic rod'and baked on as an attenuation material usable in the microwave region. At pages 752 and 757 to 763 are described metallic films on glass tubing and on dielectric carriers as inserts and as attenuator pads. 'The thin metallic films are adhered by chemical deposition, cathode sputtering, spraying, etc. Precision is accomplished by a burn-on method or by an evaporation method. The burn-on method of a noble metal consists of its application and its reduction with heat. The evaporation method consists of metal salts in a vehicle applied by painting, spraying, brushing or wiping'on glass or the like, and applying heat toevaporate the vehicle and to reduce the salt to a metal adhered'to the glass by'heating until the glass softens.

Also described are metallic mixtures of platinum, palladium and rhodium which also are applied to glass rods andare'baked.

A brief summary of'the invention follows indicating its nature and substance together with a statement of the object of the invention commensurate and consistent with the invention as claimed and also setting out to exact nature, the operation and the essence of the invention complete with proportions and techniques that are necessary with its use. The purpose of the invention also is stipulated. The presentation is adequate for any person who is skilled in the art and science to which the invention pertains to use it without involving extensive experimentation. The best mode Of'carrying out the invention is presented by the citing of a specific operative example inclusive of the preparation and the use of at least one example of'the invention.

The present invention consists of a polystyrene rod with a main midsection between two compensating sectionsat the opposite ends of the rod. The compensating sections are plated with bismuth, nickel or the like. Wire leads are connectedwiththe metal plates through a highly 2,895,117 Patented July 14, 1959 conductive material such as silver at the edges of the compensating sections at opposite ends of the main section.

Styrene is an organic compounds consisting of a benzene ring to which an ethylene group is attached,

c l-ncnzcm. Polystyrene is styrene polymerized to a desired degree. Nickel is an experimentally confirmed alternate for bismuth in the device that is contemplated hereby, excepting for its limitation that it is reactive with filaments to be described hereinafter, thereby restricting its deposition in a plating operation to its vaporization out of contact with the filaments.

The purpose of the developmental work out of which the present invention arose was to ruggedize an attenuator insert construction with the object of increasing its resistance to physical shock while maintaining or improving the electrical characteristics of the insert during its service in anattenuator.

In the experimental work leading up to the present invention various metals were tried, such as silver, silver alloys, copper, aluminum, iron, nickel, bismuth, etc. The metals were plated on various dielectric materials such as a styrene polymer, a tetrafiuoroethylene polymer, polybasic organic acids esterified with polyhydric alcohols, resins, etc. Out of this experimental work, a satisfactory attenuator insert developed was a polystyrene rod coated with bismuth on compensating sections at opposite ends of the 'rod and on either side of the main section.

Commercially available polyesters also provided experimentally satisfactory insert rods.

The'object of the present invention is to provide a new and an'improved attenuator insert which is characterized by 'physicaland electrical characteristics which are superior to those of any comparable attenuator insert which has been previously available, under standard conditions of temperature and pressure.

In the accompanying drawings:

Fig. l is a side elevational view of an attenuator insert which embodies the present invention; and

Fig. 2 is a sectional view taken along the line 22 of Fig. 1 looking in the direction indicated by the arrows.

The attenuator insert which is contemplated hereby comprises a rod 1, which preferably is made of polystyrene or the like, with thinly metal plated compensating sections 2 and 3 at opposite ends of the rod and interposed therebetween a main section 4. The metal plates of the compensating sections 2 and 3 preferably are of bismuth or the like. On either end of the main section 4 is a band of electrically highly conductive material, such as the silver bands 5 and 6 in electrical contact with the adjacent compensating sections 2 and 3 respectively. Electrically conductive wires 7 and 8 are in electrical contact with the silver bands 5 and 6 respectively. The wires 7 and 8 terminate in free end leads '9 and 10 which are available for making electrical contacts through the silver bands 5 and 6 with the metal plates on the compensating sections 2 and 3 of the attenuator insert, respectively throughout. The silver bands preferably are appliedin the form of powdered silver pigment dispersed in a vehicle which solidifies to a bonding medium when heated. Metal bullets 11 and 12, electrically connect to the remote ends of the compensating sections 2 and 3, respectively, and mechanically attached to opposite ends of the rod 1 provide for the insertion of the fixed-value attenuator pad, or the attenuator insert, into the metallic center conductor of a coaxial-line system with which the device is to be used, as explained in paragraph 12-12 on page 757 of volume 11 of the previously cited Radiation Laboratory Series text.

In making the attenuator insert which is contemplated hereby, the plastic rod 1 is cut to apredetermined length. The rod is cleaned with soap and water and it is then 2,895,117 f Y e rinsed with clear water and is dried under an air blower under standard conditions.

Three areas of constant resistance are then defined along the insert by the boundary line strips 5 and 6 of powdered silver in a vehicle. The boundary defining strips are caused to encircle the rod. Lengths of fine copper Wire 7 and 8 are Wrapped over the silver strips and'secured firmly in place. Wire contacts leads 9 and it) remain extending out from the structure as connectors for the making of resistance measurements for the insert. Depending upon the character of the vehicle in which the silver powder is dispersed, the silver powder may be bonded to the polystyrene rod by a drying operation at room temperature and pressure or, where so desired, the assembly may be oven baked or the like, for strongly adhering the powdered silver to the surface of the polystyrene rod, both of which methods are common practices in the paint and varnish industry.

The attenuator insert, bearing the silver strips 5 and 6 contacted by the wires 7 and 55, respectively, is then placed Within a bell jar or other compartment adapted for the vaporization of metals therein. The compartment is then evacuated to a degree adequate for accomplishing metal plating and a relatively heavy plating of metal is deposited on the entire length of each attenuator insert within the compartment. The deposition of the metal may be accomplished by commonly available methods and illustratively may be vaporized from boats made of tungsten. Where the coating on the compensating sections is to be of the metal bismuth, bismuth wire may be cut into pieces, each of which is about 5 to 7 millimeters long. The pieces of bismuth wire are bent to U-shape and are hung on a tungsten wire helix from which the metal is vaporized by electrically energizing the tungsten helix. This procedure is not adapted for the deposition of nickel plate on the surface of the assembly because of the reactivity between the elements nickel and tungsten, but it is applicable to the deposition of bismuth.

Each section of the attenuator insert so made is then hand buffed with strips of a suitable material such as paper, cellulose or the like, acting as an abrasive and it is by means of this buffing that the resistance of the three sections of the insert is accomplished. Bismuth is of a hardness between that of gysum and calcite. Periodically during the bufiing operation the resistance of each section is measured until a desired resistance is accomplished for each section of the insert. The buffing procedure permits the easy and the accurate adjustment of the resistance value of each section of the insert.

Where preferred, each section of the insert so made and tested under standard conditions of temperature and pressure may be caused to have its own fixed resistance value independently of the resistance values of the other sections of the insert. Illustratively the resistance of each of the end compensating sections of the insert may approximate 30 ohms and the resistance of the middle or the main section may aproximate 50 ohms.

The plated metal on the end or the compensating sections of the insert is deposited relatively heavy as compared with the plated metal on the middle or the main section. In a high vacuum vaporized metal travels in straight lines. As a consequence in practicing the method which is contemplated hereby the tungsten boats or the helix is placed so that approximately predetermined amounts of metal are deposited on the ends of the compensating sections of the insert. The overlapping paths of the vaporized metal on the surface of the main section 4 of the insert may result in excessive metal depositions which may be reduced in thickness or which may be removed by bufling or by etching as preferred. With constant length the resistance of a metal varies inversely with its cross section.

Upon the completion of the bufiing operation to predetermined resistance values, the finished surfaces are protected from abrasion by the application thereto of a synthetic resin, a varnish or the like. The synthetic resin or the varnish used must consist of both a pigment and a vehicle which are substantially chemically inert to both the plastic rod and to the metal plate which is adhered to the plastic rod. Illustrative synthetic resins are listed on pages 16 to 20, inclusive, in Synthetic Resins and Rubbers by Paul 0. Powers, published in 1943 by John Wiley and Sons, New York city, New York, and in subsequent publications. An illustrative satisfactory varnish which may be applied under room conditions of pressure and temperature consists of 14 grams of a synthetic resin such as coumarone, dissolved in 25 cubic centimeters of amyl alcohol. This varnish provides an excellent protective coat which is dried under illustratively an atmosphere of pressure and up to that tem perature at which either the plastic rod or the metal plated to the plastic rod, or the silver band bonded to the plastic rod, sufiers deterioration.

A procedural modification in method is the etching off of the plated metal from the sections of the insert. Illustrative etching solutions are by Weight 30% hydrochloric acid, 25% nitric acid or 40% acetic acids in water. The etching of the plated metal is accomplished by either immersion or by swabbing, followed by rinsing in running water and then in alcohol. The defined etchants raised the resistance values of the sections of the red at rates based on the chosen etchant, its concentration and the period of time during which the acid dissolves the plating metal on the polystyrene rod.

I The described methods and the products embodying the present invention have the following advantages: (1) they produce non-inductive resistances of accurately controlled values from zero to infinity resistance; (2) they produce resistances which minimize capacitive'etfects by permitting metal plating values of extreme thinness; (3) they produce metallized impedance inserts which may assume substantially any desired geometric configuration;

and (4) they produce impedance inserts which are characterized by non-inductive resistance values which may be varied continuously in either linear or in irregular patterns.

It isto be understood that the rod, silver strip, Wire and the bismuth coated sections of the attenuator insert and the described methods by which the insert is made, have been submitted as illustrative embodiments of the present invention and that similar modifications may be made therein without departing from the scope of the present invention.

What I claim is:

1. A ruggedized attenuator insert comprising a solid polystyrene rod with a bismuth coat permanently and firmly adhered to the rod surface throughout its length and the bismuth coat axially divided into three sections of predetermined resistive fixed values, a first compensating section, a second compensating section, a main section intermediate the first and the second compensating sections, and a pair of electrical contacts shunting the main section.

2. The attenuator insert defined in the above claim 1 inclusive of a first electrically conductive ribbon of silver bonded to the bismuth coat at the junction of the first compensating section with the main section, and a second electrically conductive ribbon of silver bonded to the bismuth coat at the junction of the second compensating section with the main section.

3. The attenuator insert defined in the above claim 2 inclusive of a first wire conductor connected electrically through the first conductive silver ribbon with the first compensating section bismuth coat, and a second wire conductor connected electrically through the second conductive silver ribbon with the second compensating section bismuth coat.

4. A ruggedized attenuator insert comprising a polystyrene rod, a coat of the metal bismuth firmly and permanently bonded to the outside surface of the rod throughout its length and the bismuth coat being axially divided into three sections, two strips of metallic silver adhered to the bismuth coat on the rod at the opposite ends of the midsection, and a conductive wire loop around each silver strip on the polystyrene rod and terminating away from the rod in an electrically conductive wire lead.

5. The method of making a three section attenuator insert comprising selecting a hollow cylindrical polystyrene rod of predetermined dimensions, cleaning and drying the rod, positioning the rod within a compartment which can be evacuated and which is provided with means for vaporizing a metal, substantially evacuating the compartment, releasing within the evacuated compartment a vaporized metal and causing the deposition on the rod of the metal as a plate, removing the plated rod from the compartment, removing from each insert section sufficient metal plate to establish a predetermined resistance value therefor applying a silver band on either end of a main section substantially midway between the opposite ends of the hollow rod with the silver bands in electrical conducting contact with the metal coat on the rod, inserting a pair of metal bullets into the opposite ends of the tube, and maintaining taut between the metal bullets a centrally positioned electrically conducting wire substantially continuously throughout the length of the rod as a metallic center conductor in a coaxial line system.

6. The method defined in the above claim together with the further step of applying a protective layer to the surface of the plated rod.

7. The method defined in the above claim 5 inclusive of looping and securing in electrical conducting contact with the silver band an electrically conductive wire contact as an available outlet around each silver band on the rod.

8. A ruggedized attenuator insert comprising an electrically nonconductive rod, a plate of nickel on the outside surface of the rod substantially throughout its length, a pair of rings of silver plated on the nickel plate at opposite ends of a main section axially interposed between the rod ends, and a wire making electrical contact with each of the silver plate rings.

9. The attentuator defined by the above claim 8 protectively coated with a varnish.

References Cited in the file of this patent UNITED STATES PATENTS 1,388,373 Richtmyer Aug. 23, 1921 2,036,368 Siegel et al. Apr. 7, 1936 2,357,473 Jira Sept. 5, 1944 2,549,775 Charchian Apr. 24, 1951 FOREIGN PATENTS 527,280 France Oct. 22, 1921 537,085 Great Britain June 9, 1941 

1. A RUGGEDIZED ATTENUATOR INSERT COMPRISING A SOLID POLYSTYRENE ROD WITH A BISMUTH COAT PERMANENTLY AND FIRMLY ADHERED TO THE ROD SURFACE THROGHOUT ITS LENGTH AND THE BISMUTH COAT AXIALLY DIVIDED INTO THREE SECTIONS OF PREDETERMINED RESISTIVE FIXED VALUES, A FIRST COMPENSATING SECTION, A SECOND COMPENSATING SECTION, A MAIN SECTION INTERMEDIATE THE FIRST AND THE SECOND COMPENSATING SECTIONS, AND A PAIR OF ELECTRICALS CONTACTS SHUNTING THE MAIN SECTION. 